Passive acoustic liners for aero-engine noise control: A review

Aero-engine noise reduction has always been a critical challenge in the field of science and engineering. Passive acoustic liners are considered one of the most effective structures for reducing aero-engine noise, significantly improving comfort aboard aircraft, protecting personnel health and reducing the noise footprint of aircrafts. This review summarizes the progress in passive acoustic liners, including locally reacting liners, non-locally reacting liners and metamaterial liners. We provide an overview of the fundamental structures, performances, and absorption mechanisms associated with these liners. Firstly, we briefly introduce the absorption mechanism of locally reacting liners and non-locally reacting liners respectively, and summarize the different types of each. Secondly, the unique ways in which acoustic metamaterials control sound waves due to their negative physical parameters are illustrated. Furthermore, we review the applications of acoustic metamaterials in passive acoustic liners. Finally, the challenges and opportunities of passive acoustic liners are analyzed and prospected.